This invention relates to the field of closed-loop feedback control systems having a human operator or other living biological specimen incorporated in the closed loop, and having disturbance or noise functions present.
Instances wherein human beings, primates, or other living creatures are situated in closed-loop electromechanical feedback systems occur frequently in present-day technical apparatus. Examples of human-involved feedback arrangements include the thermostat controls of an environmental temperature regulator e.g., a furnace or air conditioner in a house, an electric blanket with temperature controls, a pinball machine or video game and the operation of automobiles, boats and aircraft. In each of these faeedback systems the human or biological specimen serves as a controller of a relatively large energy delivery system and employs one or more of the human senses in performing the controlling operation and closing a feedback loop. Human temperature sensitivity is employed in the first of these examples, while sensitivity to visual, audible and other stimuli are employed in the latter and more complex examples. In the medical art, examples of human feedback arrangements and abnormal conditions which interfere with the operation of these feedback arrangements are found; these arrangements include the acts of eating and moving objects by human manipulation. In this field there is also encountered the disruption of intended feedback arrangements by infirmities such as Parkinson's disease, where a noise or extraneous interference signal is imposed on normal feedback loop functioning.
A particularly demanding example of a feedback system involving a human operator is found where a moving vehicle is required to track a predescribed course or an externally-determined trajectory a trajectory that imposes resolution and response frequency parameters approaching the limits of human operator capability. A notable specific example of this type is found in the demands placed on the pilot of a modern high-performance aircraft such as the currently used F-15 and F-16 fighters and by the flight simulators used to train and test these pilots. These aircraft are in addition capable of subjecting a pilot to acceleration forces or G field forces of several times the force of gravity and moreover of inducing these G forces along a plurality of coordinate axis directions during tracking or other maneuvering departures of the aircraft from straight level flight. The magnitude and direction of the G forces developed in present-day aircraft has reached the range of posing a threat to the ability of a human operator to adequately control the feedback system (i.e., the aircraft), in an optimum and safe manner.
Numerous examples of feedback systems involving control by a human operator are also found in the patent art. These examples include the patent of George E. Crawford, Jr., U.S. Pat. No. 4,158,196, which is concerned with a man-machine interface system such as might be used in controlling the movements of a wheelchair. In the Crawford patent the controlling signals are derived from electrodes placed on the body of the wheelchair occupant so as to respond to muscle stimulus signals or alternately are arranged to respond to some predetermined code, such as Morse code generated by the controlling subject. The Crawford apparatus is of the type providing open-loop control of the work member except for the loop closing provided by the human subject. The Crawford apparatus appears principally concerned with avoiding a manual force input apparatus for the electrically operated control system.
An arrangement employing force feedback in a control system is shown in the patent of Carl F. Ruoff, Jr., U.S. Pat. No. 4,278,920, which concerns a workpiece manipulator such as might be employed in the machine tool art. According to the Ruoff invention, the work positioning servosystem is programmed by recording and re-using the control parameters generated during a manual transfer of the workpiece between two work positions, the manual transfer events being sensed by a collection of position and force responsive transducers. The Ruoff patent appears principally concerned with the addition of force signals to the previously used position signals in achieving this servo programming operation. The Ruoff patent appears unconcerned with the forces observed by the human operator of the servosystem or with the generation of forces which will aid the human operator in performing a transfer or tracking operation.
An example of a control system which accommodates both a human operator and the characteristics of an aircraft is found in the patent of Carl D. Griffith et al., U.S. Pat. No. 4,345,195, which concerns an improved servoactuator apparatus for an aircraft such as a helicopter. The Griffith patent is concerned with the servosystem used to operate control surfaces of the helicopter in response to the pilot's movement of the helicopter control stick. To this end, the Griffith apparatus includes a servo-controlled "feel" spring which provides the pilot with a manual indication of forces being exerted by the aircraft control surfaces. This is in similarity to the feeling experienced by a pilot operating an aircraft having only simple mechanical linkage between the control stick and the aircraft control surfaces. The force received by the aircraft pilot in the Griffith invention is related to the aircraft control surface loading, that is, to the force of the air stream engaging the control surfaces. Such forces are known in the aircraft art to relate to the airstream velocity, the control surface displacement from a neutral position, the relative attitude and velocity of the aircraft and several other factors. The Griffith patent also contemplates use of the "feel" spring as a path for applying other non feel related forces to the aircraft control stick as indicated at column 8, line 14; and column 9, line 44. In a related patent to the Griffith patent, U.S. Pat. No. 4,426,607, inventors Homer D. Black et al. describe a differential linkage apparatus which is compatible with the servoactuator apparatus of the Griffith invention.
Another control system relating to aircraft is shown in the patent of Wilhelmus J. Lam, U.S. Pat. No. 4,398,889, Which discloses improvements to a flight simulator whereby the pilot's control stick is impressed with forces representing the response of a controlled member such as an aircraft under simulated flight conditions. The signals applied to the control stick in the Lam apparatus are derived from first and second integrator circuits and are intended to provide the pilot with the correct "feel" at the control stick for the flight conditions under simulation.
An arrangement for changing the characteristics of an aircraft control stick in response to G forces sensed by an accelerometer is also shown in my prior patent, U.S. Pat. No. 4,477,043. In this patent an electric motor is used to compress a spring member that opposes movement of the control stick away from a center or neutral position. Alternate embodiments shown in this patent indicate that compression of the stick opposing spring exerts a force on the aircraft control stick--a force tending to restore the stick to a neutral position. The '043 patent does not consider the consequence of noise or muscle tremor signals originating with a pilot or arrangements for minimizing the effects of such signals in an aircraft apparatus. The disclosure of the U.S. Pat. No. 4,477,043 patent is hereby incorporated by reference herein.